I bought a 07' 328i with 53k of the ODO ,
The dealer service record stated the oil was changed a the "BMW approved" intervals, of 13k and 15 k

I changed the oil and found that I have sludge deposits forming on the inside valve cover, you can stick you finger in and lightly wipe off bits of coked on oil and sludge particulate.

I was surprised to see this, since I have owned 2 other bmw's an 87 and a 94, both with over 230k and have never found sludge in either engine,
Even when I disassembled the m20 motor from my 87' with 245k on the clock ,the engine was spotless. MY Volvo 240 with 310,000 commuter miles is spotless , even my 91 mustang that only sees short trips and heavy drag racing has never had sludge or even coking

I s/w the my serviced advisor, he "advised" me this was normal. NORMAL ?! what is normal about sludge in a hi performance motor I asked. He said it is common for this car. He was unable to clarify the difference of common and normal in this situation . He said bmw had no recourse for this problem ,

I let him know that the bmw oil change policy is most likely in direct cause of the sludge problem. The SA advised there was no way to tell that since it was used there was no record of the oil changes, I prodded him memory that this car is a CPO and all the previous services were at this dealer.
Nice Try !

I will be contacting BMWNA, lets see what kind of response I get, Im sure it will be along the lines of "go f yerself, and thanks for the payments."
In the mean time I will be changing my own oil at 7-8k miles,